1. Field of the Invention
The present invention relates to a driver for driving a liquid crystal display and a method of driving the same, and more particularly to those enabling an input terminal and an output terminal for data to and from a bi-directional common driver to be fixed and further enabling a shift direction of data to be changed even after a liquid crystal display panel has been mounted.
2. Description of Related Art
Recently, mobile devices such as cellular phones has become very popular. A liquid crystal display (hereinafter, referred to as a LCD) used for such mobile devices, especially for cellular phones, includes a simple matrix type LCD, an active matrix type LCD, and so on. Pixels are lit by electrodes disposed on both vertical and horizontal sides in the simple matrix type LCD while an individual element corresponding to a pixel is turned “on” or “off” in the active matrix type LCD.
Furthermore, the active matrix type LCD includes a TFT (an abbreviation of thin film transistor) type LCD in which a transistor is provided on each pixel, a TFD (an abbreviation of thin film diode) type LCD in which a diode is provided on each pixel, and so forth. Since the TFD type LCD has similar contrast and color variation to the TFT type LCD and duplicates moving images and natural colors with low power consumption, it is expected that the TFD type LCD will be widely used for cellular phones or the like in the future.
Actually, when the LCD panel described above is mounted on a mobile device, as illustrated in FIG. 3, it is necessary to dispose, besides the LCD panel, a segment driver X (also referred to as X driver, hereinafter described as SEG driver) connected to a segment electrode of the LCD panel and a common driver Y (also referred to as Y driver, hereinafter described as COM driver) connected to a common electrode, in a housing. Specifically, in a cellular phone or the like, in view of a layout of a LCD display face on a surface of a housing, the SEG driver X is often disposed below the LCD panel, and the COM driver Y is often disposed on the left of the LCD panel (illustrated by a solid line in FIG. 3) or on the right thereof (illustrated by a chain double-dashed line in FIG. 3).
In order to display by scanning the LCD panel from the top to the bottom, if the COM driver Y is disposed on the left of the LCD panel, as will be understood from the later description, input data from the SEG driver X needs to be input to an input/output terminal DYIO1, and if the COM driver Y is disposed on the right thereof, the input data from the SEG driver needs to be input to input/output terminal DYIO2 since the COM driver Y is disposed upside down.
Accordingly, in order to scan the LCD panel sequentially from the top to the bottom irrespective of the position of the COM driver, (on the left or the right of the LCD panel), the COM driver should be bi-directional (two directions, one from a shift register output line 1 to a shift register output line 120, and the other from the shift register output line 120 to the shift register output line 1) so that a shift direction of the COM driver can be reversed.
In view of such a necessity, a bi-directional COM driver that enables the shift direction to be controlled by a control signal and has the first and the second input/output terminals DYIO1 and DYIO2 whose input/output relationship can be reversed in accordance with the shift direction has been developed.
FIGS. 4(a) and 4(b) show a bi-directional COM driver (a driver IC). The bi-directional COM driver incorporates a shift register circuit (not shown in the drawings) having a predetermined number (120, in the figure) of flip-flops. Accordingly, the bi-directional COM driver has 120 shift register output lines 1 through 120.
In addition, the bi-directional COM driver has the first and the second input/output terminals DYIO1 and DYIO2 whose input/output relationship is reversed in accordance with the shift direction controlled by a control signal SHF.
Therefore, if the shift direction is in a first direction shown in FIG. 4(a), the first input/output terminal DYIO1 becomes an input terminal to which input data is input and the second input/output terminal DYIO2 becomes an output terminal from which output data is output by applying, for example, a high level (hereinafter H level) signal to the bi-directional COM driver as the control signal SHF.
In this case, the bi-directional COM driver starts a data shift operation in response to the input data inputting to the first input/output terminal DYIO1, and then sequentially outputs shift data (corresponding to LCD scanning data) with the shift direction from the shift register output line 1 to the shift register output line 120. Then, the bi-directional COM driver outputs the output data from the second input/output terminal DYIO2 when a sequence of data shift to the output line 120 has finished.
If the shift direction is in a second direction as shown in FIG. 4(b), the first input/output terminal DYIO1 becomes the output terminal from which output data is output and the second input/output terminal DYIO2 becomes an input terminal to which input data is input by applying, for example, a low level (hereinafter L level) signal to the COM driver as the control signal SHF.
In this case, the bi-directional COM driver starts the data shift operation in response to the input data inputting to the second input/output terminal DYIO2, and then sequentially outputs shift data with the shift direction from the shift register output line 120 to the shift register output line 1. Then, the bi-directional COM driver outputs the output data from the first input/output terminal DYIO1 when a sequence of data shift to the output line 1 has finished.
However, when the above-mentioned bi-directional COM driver is disposed, for example, on the left of the LCD panel placed in a housing of a device (see, the arrangement illustrated by the solid line in FIG. 3.), in order to display by scanning the LCD panel from the top to the bottom, it is necessary to arrange the wiring so that the input data from the SEG driver X (the data providing a trigger for beginning the data shift operation) is supplied to the first input/output terminal DYIO1 placed in an upper position of the COM driver. Accordingly, since the position to which data is input from the SEG driver is fixed after the LCD panel has been mounted, the shift direction of the COM driver is fixed in a direction from the top to the bottom (in the case of the arrangement illustrated by the solid line in FIG. 3), so that the shift direction can not be changed after the LCD panel has been mounted. For example, when the LCD panel needs to be scanned from the bottom to the top, the wiring has to be changed so that the input data from the SEG driver is input to the second input/output terminal DYIO2, which is impossible after the LCD panel has been mounted.
In view of the above problem, the present invention is intended to provide a driver for driving an LCD and a driving method thereof that enable the input terminal and the output terminal for data to and from the bi-directional COM driver to be fixed as well as the shift direction of data to change even after the LCD panel has been mounted.